The cause of the F-22 Raptor's oxygen woes has been discovered - a tiny valve

IT has cost the life of a combat pilot and shackled the United State's most advanced jet fighter. After months of denial, dispute and frantic study - the fault has been found.

News Corp Australia NetworkJuly 26, 20121:47pm

A The Lockheed Martin/Boeing F-22 Raptor jet flies during an air display at the Farnborough International Airshow. Picture: AFP / BEN STANSALLSource:AFP

IT has cost the life of a combat pilot and shackled the United State's most advanced jet fighter. After months of denial, dispute and frantic study - the fault has been found.

The US Air Force's fleet of F-22 Raptors has been beset by oxygen deprivation problems affecting its pilots since 2010.

With claims of cover-ups, groundings and expensive new filters being fitted - then stripped after turning pilots' lungs black - the cause has finally been uncovered: A small valve fitted to combat vests specifically designed to be worn in the Raptor.

The faulty pressure-suit valve is being blamed for causing more than a dozen pilots to become dizzy, disorientated and even blackout since 2008.

The flight suits would inflate - and stay inflated - under conditions they were not intended to do so.

The $80 billion Raptor fleet had been under strict flight restrictions since May after being grounded for four months last year. They were only allowed to fly at low altitudes where additional oxygen was not needed.

Those restrictions have now been lifted.

The US Air Force has steadfastly denied any problem with the super fast and super stealthy fighter's oxygen systems. At least one fatal accident linked to oxygen deprivation has been officially blamed on "pilot error", even though telemetry clearly showed the pilot had fallen unconscious in his cockpit.

Two pilots who spoke out in the media about being forced to fly the fighter despite safety fears have been placed under a government whistle-blower protection program.